Extended market hours data is available from 4:00 AM to 8 PM ET for US markets with the Pro plan and above. The data can be retrieved via API at the 1min, 5min, 15min, and 30min intervals. Alternatively, it can be streamed via WebSocket.
/time_series, /quote, /price, and /eod endpoints support pre-/post-market data while passing &prepost=true parameter.